[Talk-us] Complex intersection mapping

stevea steveaOSM at softworkers.com
Tue Oct 15 18:13:06 UTC 2013

I just want to emphasize that there are (at least) two separate but 
related issues here:

1)  Whether the "before" or "after" style is preferred or more correct,
2)  What a routing algorithm (potentially yet-to-be-coded or 
now-actually coded) does with either or both.

Regarding 1), it appears that we have proponents for both styles.  In 
OSM, I submit "that's just gonna happen."  While consensus is a 
beautiful thing, it is not always perfectly achievable.  I don't 
believe it (entirely) reasonable to, say, have a bot go through 
thousands of intersections and "make them" one flavor or another, 
simply to make a routing algorithm more happy or easier/faster to 
complete.  Maybe a case could be made for that, but I'd like to hear 
it.  (I think of it as a BIG maybe).

Regarding 2), be smart about (algorithmically handle) both flavors of 
intersections.  Or even more.  This is a "tip of the iceberg" problem 
that likely requires more research and a classification into more 
than simply two flavors of intersections.  I think it possible that 
given the universe of possibilities, there are smart and clever ways 
to apply a routing algorithm:  this is just geometry and computer 
science after all (points, vertices, and an executive that rides 
along the geometry which probes around, backs out, and yields 
results).  Research the entirety of the problem domain, invest 
(substantially, if necessary) in the algorithm to handle most/all 
cases, and all can be well.

While it is fine to discuss "better methods" (note that is plural) of 
creating complex intersection geometry, I find it stifling to do so 
in the context of "for a particular routing algorithm."  That leans 
heavily towards "coding for the routing algorithm," and I think we've 
learned that such coding make the underlying data not all they can be 
(i.e. well-formed and as correct as we are able to observe and enter 

I seem to be echoing what Minh said near the end of his reply: 
"handle both." (or more).

Good discussion.


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